For UWP settings, the user can choose DX12 as the only Graphic API.
However, the DX12 is experimental and should always paired with DX11 in the setting.
Besides, on the Windows standalone side, if user chooses DX12 as the only option, the Editor generates a warning and automatically add DX11. The behavior should be consistent for both standalone and UWP.

Repro Step:
1. Go to Player Settings -> Other Settings -> Graphics API, make sure it is for UWP
2. Uncheck the "Auto Graphics API"
3. Add "Direct3D12 (Experimental)" and delete "Direct3D11"
4. Observe the Editor does not complain or correct it.
(Optional) 5. Repeat step 2-4 for the Standalone Graphics APIs for Windows and observe the warning message in Editor Console

Expected: The experimental DX12 should not be the only Graphics API chosen.